Proteins are the most abundant macromolecules in cells, making up over half their dry weight. Proteins and peptides are known to carry chemical information in their tertiary structures. A number of proteins occurring in nature are conjugated to other chemical groups. Examples are lipoproteins, glycoproteins, phosphoproteins, hemoproteins, flavoproteins, and metalloproteins.
Proteins have diverse biological functions. Non-limiting examples are transport proteins (e.g., hemoglobin and serum albumin), nutrient and storage proteins (for example, gliadin, ovalbumin, casein, and ferritin); contractile or motile proteins (e.g., actin, myosin, tubulin, and dynein); structural proteins (for example, keratin, fibroin, collagen, elastin, and proteoglycans); defense proteins (e.g., antibodies, immunoglobulins, fibrinogen, thrombin, botulinus toxin, diphtheria toxin, snake venom, and ricin); enzymes, and regulatory proteins (e.g., insulin, growth hormone, corticotropin and repressors). Molecular imprinting techniques can be used to prepare a wide variety of mimics of these important compounds.
Among common constituents, the phosphate group is involved in many biomolecules, including proteins, lipids, carbohydrates and nucleic acids. Selective enrichment and derivatization of phosphate groups are important tools to analyze these biomolecules. For example, phosphoproteins are often present in compounds at low levels, thus a selective enrichment and labeling technique is essential to achieve detection.
Currently, enrichment and labeling of phosphoproteins is done in separate steps. Immobilized metal affinity chromatography and phosphor specific antibody resin are two standard tools for enriching phosphoproteins. Beta-elimination followed by Michael addition is commonly used to derivatize phosphate groups for improved detection sensitivity in mass spectrometry.